Too often forgotten, network load balancing may be a high-availability lifesaver in your Windows environment

InfoWorld|Apr 4, 2012

Admins seeking a secret weapon in Windows environments should look no further than network load balancing, an often underutilized capability built right into Windows Server, and one that's easy to take advantage of.

Primarily used for stateless applications, such as a Web server running IIS (Internet Information Services), NLB can be put to work in a variety of settings to leverage high availability and load balancing in otherwise unconsidered spots. Here's a look at what makes NLB tick and where you can take advantage of its underlying power.

The value of network load balancingNLB's value resides in clustering. With it, you can create a cluster of machines aimed at providing high availability and load balancing. The concept is simple: Rather than point to a specific system, you configure your DNS record to point at an NLB cluster's FQDN (fully qualified domain name). Assuming the cluster has two or more servers responding to a given request, NLB ensures the load is evenly distributed to each server; in the event of a failure, NLB directs requests to the remaining functional servers. From the client or user perspective, the transition is seamless (although the experience does depend on the application, the protocol, the affinity settings and the nature of the transition).

NLB's simplicity is what differentiates it from other clustering solutions such as failover clustering in Windows Server Enterprise Edition. Foremost is the fact that NLB does not use clustered storage devices, like a shared storage array. Each server runs a copy of the IP-based application or service, and the data for those applications or services is held on the local machines. It's not active/passive clustering; instead, all machines in the cluster can function and serve clients equally to balance the load.

NLB can be used with a single network adapter, but the better setup uses two network adapters to separate the NLB network from your public LAN. Some admins wonder whether RAID is necessary for these systems. Because each NLB member is an exact clone with identical data, RAID isn't required. In many cases, servers in the cluster are providing services, not necessarily data itself; again, RAID or fault-tolerant disks aren't the most important concern.

Where to take advantage of network load balancingNLB provides obvious benefit to websites with IIS. With NLB, you can scale out to 32 servers. Other IP-based applications and services can also benefit from NLB, including media servers, terminal servers, and e-commerce sites.